maybe bubble?
Bubble doesn't have a tie to Firey.
Woody has a tie to all four, small or big:
Firey - An enemy. (WIJTTEFET)
Blocky - It's obvious. (BFDI, BFB)
Leafy - The reason he got chipped. (BFDI 1a)
Flower - Kicking him off the balance beam. (BFDI 1a)
However, in the new ONaFA (One Night at Firey's Again) trailer, Snowball and TV are shown.
Snowball probably has something in the old comics, but I can't think of TV, at all. I'm pretty sure he hasn't met doesn't even know TV!
So, let's look for another character who has some sort of connection to Firey, Leafy, Blocky, Flower, Snowball, and TV. TV makes it VERY hard since he knows pretty much nobody.
But, I just figured it out. Pen. He knows all of these guys.
So there you have it, as far as my theory goes, Pen is the night guard.